Stylus actuated electrical device and electrical kit including same

ABSTRACT

Described is a stylus-actuated electrical device including a printed circuit board and an overlying flexible impression sheet, both carrying an electrically conductive pattern. The two conductive patterns are normally insulated from each other by a coating of a soft, pressure-flowable, tacky, insulating material, such as wax. When &#39;&#39;&#39;&#39;writing&#39;&#39;&#39;&#39; with a stylus, portions of the two conductive patterns are brought into contact with each other along the line of write, which contact is broken by separation of the impression sheet, as in a &#39;&#39;&#39;&#39;Magic Slate&#39;&#39;&#39;&#39; device. Both conductive patterns are in the form of discrete conductive deposits each insulated from the others on all sides by narrow interruptions, such that a conductive pathway is formed by the successive electrical contacts between the conductive patterns of the two members under the pressure of the stylus, the conductive deposits of one member bridging the interruptions of the other along the line of movement of the stylus. Also described is a kit including the stylus-actuated electrical device and a plurality of selectively insertable electrical components enabling various electrical circuits to be produced in a simple manner by drawing same with a stylus, and to be erased in an even simpler manner by merely separating the impression sheet from the printed circuit board.

United States Patent [1 1 Barish Oct. 21, 1975 STYLUS ACTUATED ELECTRICAL DEVICE AND ELECTRICAL KIT INCLUDING SAME [76] Inventor: Benjamin J. Barish, 36 Yehuda Hanassi, 36 Yehuda l-lanassi St., Israel [22] Filed: Mar. 1, 1974 [21] Appl. No.: 447,333

Related U.S. Application Data [63] Continuation-impart of Ser. No. 265,985, June 26,

1972, abandoned.

[30] Foreign Application Priority Data June 30, 1971 Israel 37197 [52] US. Cl. 178/18; 355/66; 346/21 [51] Int. Cl. Gllc 5/02; G091) 23/18 [58] Field of Search 35/9 C, 19 A, 6|, 62, 63,

35/66;178/18, 19, 20; 339/18 R, 18 B, 18 C, 18 P", 235/61.11 H, 61.12 C; 346/21 Primary Examiner-Thomas A. Robinson [57] ABSTRACT Described is a stylus-actuated electrical device including a printed circuit board and an overlying flexible impression sheet, both carrying an electrically conductive pattern. The two conductive patterns are normally insulated from each other by a coating of a soft, pressure-flowable, tacky, insulating material, such as wax. When writing with a stylus, portions of the two conductive patterns are brought into contact with each other along the line of write, which contact is broken by separation of the impression sheet, as in a Magic Slate device. Both conductive patterns are in the form of discrete conductive deposits each insulated from the others on all sides by narrow interruptions, such that a conductive pathway is formed by the successive electrical contacts between the conductive patterns of the two members under the pressure of the stylus, the conductive deposits of one member bridging the interruptions of the other along the line of movement of the stylus. Also described is a kit including the stylus-actuated electrical device and a plurality of selectively insertable electrical components enabling various electrical circuits to be produced in a simple manner by drawing same with a stylus, and to be erased in an even simpler manner by merely separating the impression sheet from the printed circuit board.

10 Claims, 7 Drawing Figures US. Patent Oct. 21, 1975 Sheet 1 of 2 U.S. Patent Oct. 21, 1975 Sheet 2 of 2 FIG.7

STYLUS ACTUA'TED ELECTRICAL DEVICE AND:

ELECTRICAL KIT INCLUDING SAME RELATED .IJATENT APPLICATIONS The presentapplication is ancontinuation-in-part of 5.

my copending US. Pat; application No. 265,985 filed June 26, 1972' for"S-tylus Actuated-Electrical :Devices, which application, now abandoned,'was=;re

placed by continuationapplication No. 490,682 filed,

July 22, 1974. I

The presentinventionrelates, to a stylus 'actua-ted electrical device; and also to an electrical kit including I such device. I 31 r In my co-pending "'U.-S. Pat, application Ser. No. 265,985 filed June 26', 1972*(now abandoned and replaced by continuation'application :NQ. 49O,682, filed July 22, 1974;as noted-above), there is disclosedan.

in a manner somewhat resembling the mode-=ofroperation of the 'well-known Magic Sla'te.-Briefly, the device includes a supportingmember, such as a printed circuit board, "carrying one or" more electricallyconductive elementsganda, flexible impression sheet carrying other electrically-conductive elements placeable on top of the supporting member with the conductive elements of-both facing each other. A coating of wax- (or other equivalent material), on one or both of the members insulates the conductive elements from each other. Under the pressure of a-st-ylus,:hbwever., the wax parts-thereby bringing the conductiveelements of the flexible sheet'into contact with-the conductive elements of the. printed .circuitlboard. Theiwax coating, being tacky, maintains the electrical contact when .the stylus is removed, but the-contact is easily-broken ,by separation of the flexible impression sheet fromzthe printed circuit board. i

The above-cited patent application describes a number of stylus-actuated,electrical-devices operating-in oftheconductive'deposits of thesupporting member,

thereby"enabling-electrical circuits to be traced by the stylus to the various *component' terminals.

--A device is thusLproVided in'which any desired conductive pathwayimay-b e easily traced by a stylus to selected terminals*,:"'and:may justas easily be erased by merelysepa-rating the overlying impression'sheet, from accordance with the above principle,--including-an electrical switching device, agraphic input:device, and a L stylus-actuated display system. Y

BRIEF SUMMARY OF THE PRESENT INVENTION The present invention describes new forms and applications of such stylus-actuated electricaldevices.

According to one. aspect of the presentinvention, the conductive elementsaon both the' supporting member and the overlying flexible sheet memberareinthe form of discrete conductive deposits each insulatedfrom the others onlall sides by. narrow interruptionsswhen used as described above, .a conductive-pathway ,is formed 5 bleslieet from the supporting member.

Preferably, the supportingmemberis aqprinted circuit board. f,

f I According to a further feature, the device includes a plurality of electrical terminals carried by the supporting member for connection to various types ofelectri cal components, the terminals being connected to} some ductive deposits 6 each insulated from the others on all as bylformm'ga continuous metal coating on the respective members ,.and then etching-away the portions forming the interruptions. Very small interruptions can FIG-.. 5 illustrates the supporting membe'rt Sucha device may be used in many applications. I One described application is an instruction or assembly-kit 'in whicha-the terminalsare in the form of unireceiving various.electrical'components in selected arrangements. The-stylus-a'ctuated device enables different electrical circuits to be produced with these components by merely tracing the desired circuit with the stylus, and when itis desired to trace a new circuit, the -'-device can be erased bymerely separating the impreswsion sheet-from the supporting member.

electrical device actuatable by the pressure of a stylus Q BRIEF, DESCRIPTION 0F THE DRAWINGS l The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: r

" FIGQl'is' a'sectional view of the two main elements in onerform of stylus-actuated electrical device constructed in accordance with the invention;

- is a view; similar to that of FIG. 1 illustrating how a conductive pathway is formed by the use of the "30 iprinted'circu-it board in the device of FIG. 1;

F IG: 4 is aplan view of the conductive pattern on the 'overlying, flexible impression sbee t' -in the device of ILA? V V the various elements of the assembly o FIG.-1,- withfipart of the insulating coating .stripped away from the impression sheet;

FIG; 6, illustrates; how :the, interruptionsof the con- .ductivedepositson .one-memberare bridged by the =conduc-tivecleposits ofthe other when tracing the conductive pathway with the stylus; and

FIG. 7,-illustrates a circuit assembly kit constructed in accordancewith .the invention.

' "1 DEscR'IPTIoNoE THE PREFERRED v I EMBQDIMENT r Thebasic device illustrated in FIGS. 1-5 of the drawings comprises=a supporting member, generally designated 2, and a flexible-impression sheet applied thereov'er, generally designated 4. Supporting member 2 is in the form of'a printed circuit board including a rigid insulating base 5. carrying on its upper surface a conductive pattern including a plurality of discrete consides by narrow interruptions 8. The overlying flexible impression sheet 4 comprises a plastic sheet or film 10 carrying on one face another conductive pattern of discrete conductive deposits 12 each insulated from the 'others on. allsides .by narrow interruptions 14. The

.0uter1face of conductive deposits 12 on sheet 10 are covered by a-layer of wax 16.

The'conductive deposits 6 and 12 may each be applied by conventional printed circuit techniques, such thus be formed'in a very simple and inexpensive procedure. v

As shown in'FIG. 2, when a stylus is pressed against the overlying impression sheet 4, it causes the wax coating 16 to part along the line of-write of the stylus, thereby bringing the conductive deposits 12 of the impression sheet 4 into contact with the conductive deposits 6 of the printed circuit board 2 along the line of write of the stylus. The soft tacky nature of the wax coating 16 holds the conductive deposits in contact with each other upon removing the pressure of the stylus, but the electrical contact between these deposits is easily interruptable by. merely separating the flexible sheet 4 from the printed circuit board, as in a Magic Slate device.

It will be appreciated that wax coating 16 could be applied on top'of conductive deposits 6 on the printed circuit board 2 in lieu of, or in addition to, its being applied over conductive deposits 12 oni-the impression sheet 4. It will also be appreciated that other insulating coating materials could be used which are soft, pressure-flowable so asto part under the pressure of the stylus to bring the conductive deposits into contact These interruptions are somewhat exaggerated in the drawings, and in practice should be as narrow as possible, consistent with printed circuit techniques.

FIG. 4 illustrates the pattern of the conductive depos- -its 12 formed on the overlying flexible impression sheet 4. The conductive deposits 12 on this sheet are also of rectangular or square shape, with each separated from the other on all sides byinterruptions 14 which are as narrow as possible consistent with printed circuit techniques. 1

In use, the flexible impression sheet 4 is applied over the printed circuit board 2 as shown in FIG. 5, with the conductivedeposits 6 of the board and the conductive deposits 12 of the impression sheet facing each other. The layer of wax 16 on the flexible impression sheet normally insulates the conductive deposits from each other. However, when the stylus 20 (FIG. 2) is pressed against the'flexible impression sheet 4, the wax coating 16 is caused to part along the line of write of the stylus, thereby bringing conductive deposits 12 of the impression sheet into direct physical contact with conductive deposits 6 of the printed circuit board along the line of write. The physical contacts between the conductive deposits are maintained even after the stylus has been removed by virtue of the tacky nature of the wax coating 16, as in a Magic-Slate" device.

As shown in FIGS. 2 and 6, a conductive pathway is formed along the line of movement of the stylus by the successive electrical contacts between the conductive deposits of the two members, the conductive deposits 12 of sheet 4 bridging the interruptions 8 of board 2, and the conductive deposits 6 of board 2 bridging the interruptions 14 of sheet 4. This is particularly shown in FIG. 6, wherein it will be seen that each conductive deposit 12 (shown in broken lines) on the impression sheet 4voverlies a portion of several conductive deposits 6 (shown in full lines) on the printed circuit board 2 and bridges the interruptions 8 between them. The same applies with respect to conductive deposits 6 on the printed circuit board, which deposits bridge the interruptions 14 between the conductive deposits 12 of the flexible impression sheet'4. The interruptions 8 and 14 between the conductive deposits on both members should be as narrow as possible, as mentioned earlier, and in any event should be substantially narrower than the thickness of the line drawn by the stylus 20, which will thereby assure that the line drawn by the stylus will always bridge the interruptions between adjacent conductive depositsalong the line of write of the stylus.

It will be noted that the conductive deposits 6 on the printed circuit board 2 (FIG. 3) are arranged in horizontal rows and vertical columns, whereas conductive deposits 12 on the impression sheet 4 (FIG. 4), are arranged in rows and columns rotationally displaced so as to be at a bias or angle (e.g. about to the rows and columns of deposits 6. This is a preferred arrangement to minimize the possibility of an interruption 8 on the printed circuit board 2 exactly becoming aligned with an interruption 14 on the flexible impression sheet 4 when the latter is applied over the printed circuit board as shown in FIG. 5. It will be appreciated, however, that other configurations of deposits, other arrangements of deposits on the respective supporting member, and other relationships of the deposits of one supporting member with respect to the other, may be used.

It will thus be seen that the device illustrated in FIGS. 1-6 enables any-conductive pathwayto be produced by merely pressing stylus 20 against the outer face of impression sheet 4 and moving same-to trace the desired conductive pathway; and that the pathway is produced by the successive electrical contacts between the conductive deposits of members 2 and 4,- the deposits of one bridging the interruptions of the other along the line of movement of the stylus. [twill further be seen that, as in a Magic Slate" device, the so drawn conductive pathway is maintained even after removal of the stylus but may easily be erased by merely separating the impression sheet 4 from the printed circuit board 2.

Such a device may have a large number of applications. One application is shown in 7.

FIG. 7 illustrates a circuit assembly kit including the device of FIGS. l-6, which kit enables various circuits to be assembled by merely inserting selected electrical components, and drawing the necessary conductive pathways to the various components to complete the circuit. The circuit is retained as long as desired and may-be easily erased, whenever a new circuit is to be assembled, by merely separating the flexible impression sheet 4 from the printed circuit board 2. g

The kit of FIG. 7 includes a holder, generally designated 30, including the printed circuit board 2 occupyi'ngits center and surrounded by a marginal surface 32 around its four sides. The overlying impression sheet,4

is placedon top of the printed circuit board 2. in the manner described earlier, namely with conductive deposits 12 of the impression sheet facing the conductive deposits 6 of the printed circuit board but separated therefrom by the insulated coating 16 (e.g. FIGS. ,1 and The exact positioning of the flexible impression sheet 4 with respect to the printed circuit board 2 is not critical since the interruption 8 and 14 between the respective conductive deposits, being substantially narrower than the line produced by the stylus, will always be bridged by the latter lines.

The flexible impression sheet 4 may be held in place over the printed circuit board 2 in any suitable manner. For purposes of example, FIG. 7 illustrates an elongated clamping member 34 releasably secured at both ends by fasteners 36 for clamping the impression sheet 4 over the printed circuit board 2. Clamp 34 extends only along one edge of the impression sheet so that the remaining three edges are free to permit the impression sheet to be lifted in order to erase the conductive pathways formed.

The marginal area 32 of holder 30 includes a plurality of connector sockets 40 which are equally and uniformly spaced from each other. Each connector socket 40 is connected by a conductive strip 42 to one of the conductive deposits 6 of the printed circuit board 2.

The kit illustrated in FIG. 7 further includes a plurality of electrical components each having pins 44 receivable within sockets 40. Many different types of electrical components would normally be provided in the kit. A number of such components are schematically illustrated in the drawings and referred to below. Some of these components include two terminals, and some include three (and possibly four or more). In any event, the pins 44 on all the components are equally spaced, the spacing corresponding to that between the sockets 40 on the printed circuit board, so that different electrical components can be selectively inserted into various ones of the sockets 40 on the printed circuit board according to the electrical circuit to be assembled. A modular construction is thus produced providing a high degree of selectivity and interchangeability of components that may be included in the electrical circuit.

FIG. 7 illustrates only one of each of the various components, but it will be appreciated that a kit will normally include a plurality of most or all of such components, to enable assembling circuits including more than one of each type of component.

For purposes of example, FIG. 7 illustrates a resistor R, a capacitor C, a coil L, a battery B, a diode D, and a lamp M. A ground G could be permanently provided in the circuit board. Further components that may be included are a switch S, a transistor T, and various logical elements, such as an AND-gate A, an OR-gate O,

and an Inverter l.

Still further components (not shown) may be included, such as a bell to sound an alarm, a lightemitting diode to indicate the presence of a voltage, a meter to measure voltage or current, a voltage-divider having a movable tap, and the like.

Because of the modular construction, including the uniform spacing of the sockets 40 of the printed circuit board and the pins 44 of the electrical components (whether they be of the two-terminal, three-terminal, or more-terminal type), it will be seen that an almost unlimited number of different component arrangements may be inserted into the holder, and therefore an almost unlimited number of circuits may be drawn with the stylus.

Since the terminals 44 of the electrical components are connected via sockets 40 and conducting strips 42 to conductive deposits 6 of the printed circuit board, any desired conductive pathway may be produced by tracing with the stylus in the manner described above to form the electrical connections to the various components. Thus, if it is desired to connect one side of battery B to ground G, for example, it is only necessary to move the stylus to trace a path from the conductor strip 42 (or a conductive deposit to which it is connected) on the side of the battery to be grounded, to the conductive strip 42 of ground G. Terminals of other components may be similarly connected by drawing a line to the ground G conductive strip 42, or by drawing a line intercepting such a line.

In a similar manner, the terminals of the other electrical components may be connected together in any desired relationship by merely drawing the appropriate connection lines with the stylus.

The provision of a switch S is desirable, since it enables a circuit to be drawn but not to be completed until the switch is depressed. The provision of a lamp M or other indicator is also desirable since it enables the user to visually see the results of a connection. The provision of the logical elements (A, O and I) enables the respective logical functions to be demonstrated. Logical elements could be included having more than the illustrated two inputs.

Substantially no wear occurs with respect to the printed circuit board 2 and its conductors 6, but if and when the overlying impression sheet 4 wears out, it may be easily replaced by merely releasing clamp 34 and then inserting a new impression sheet. This is one of the advantages in including the wax coating 16 on the impression sheet 4.

The orientation of the impression sheet 4 with respect to the printed circuit board 2,isnot critical, as mentioned earlier, but it is important that the-interruptions 8 and 14 between the conductive deposits on the two r'nembers be as narrow as possible, and in any event, narrower than the thickness of the line drawn by the stylus. Further, the dimensions of the conductive deposits 6 and 12 are also not critical, but the larger they are, the greater will be the required spacing between the lines drawn by the stylus to avoid undesired electrical connections between drawn lines.

While the insulating coating 16 has been described above as being of wax and as being applied to the flexible impression sheet 4, it will be appreciated that it could be of other insulating material which is soft, pressure-flowable, and tacky (for example soft polyisobutylene, polyvinyl acetate, polyethyelene resins, or mixtures thereof with wax) and that such a coating could be applied over the conductive deposits 6 on the printed circuit board, rather than over the conductive deposits 12 on the flexible impression sheet 4, or together therewith.

Many techniques may be used for making the drawn lines more readily discernable. For example, a removable paper sheet can be placed over the impression sheet, and the lines drawn in ink (or pencil) on the paper sheet, the paper sheet being removed when the conductive pathway is erased by separating the impression sheet. Alternatively, the stylus used could be one which also applies a wipeable marking to the impression sheet. Further, a conventional Magic Slate could be placed over the impression sheet. Still further, the conductive deposits on the impression sheet could be in the form of milky or translucent coating (known per se), and the printed circuit board, as well as the conductive deposits supplied thereto, being of contrasting color, would thereby be viewable through the impression sheet along the line of write, as in a Magic Slate." in such an arrangement, the wax coating 16 is preferably applied on top ofthe conductors 6 on the printed circuit board.

The device could also be constructed as a large display board for demonstrating the assembly of various electrical circuits in the manner described above.

Many other variations, modifications and applications of the illustrated embodiment will be apparent.

What is claimed is:

1. An electrical device comprising a supporting member carrying at least one electrically conductive element, and a flexible sheet member carrying at least one electrically conductive element placeable on top of the supporting member with the two conductive elements facing each other, at least one of said members including a coating of insulating material to insulate the conductive elements from each other when the flexible sheet member is placed on top of the supporting member, said insulating coating being of a soft, pressureflowable material which parts under the pressure of a stylus applied to the flexible sheet member to thereby bring the two conductive elements into contact with each other, said insulating coating also being tacky to hold the two conductive elements in contact with each other upon removing the pressure of the stylus, said conductive elements on both of said members being in the form of discrete conductive deposits insulated from the others on all sides by narrow interruptions between them, such that a conductive pathway is formed along the line of they stylus pressure by the successive electrical contactsbetween the conductive deposits of the two members, the conductive deposits of one member bridging the interruptions of the other along the line of movement of the stylus, said conductive pathway being erasable by the separation of the two members.

2. An electrical device as defined in claim 1, wherein said supporting member is a printed circuit board.

3. An electrical device as defined in claim 1, wherein said insulating coating comprises wax. I

4. An electrical device as defined in claim 1, wherein the discrete conductive deposits are of polygonal shape, the deposits of one member being rotationally displaced to the deposits of the other member.

5. An electrical device as defined in claim 1, further including a plurality of electrical terminals carried by the supporting member for connection to electrical components each of said terminals being connected to one of said conductive deposits of the supporting member enabling electrical circuits to be traced by the stylus to various component terminals.

6. An electrical device as defined in claim 5, wherein said electrical terminals are uniformly spaced connectors for removably receiving various electrical components in selected arrangements to enable different electrical circuits to be produced with them by the stylus.

7. A kit including the electrical device as defined in claim 6, and a plurality of electrical components having uniformly spaced electrical terminals according to the uniform spacing of the connectors in said electrical device, said components being selectively receivable in the connectors in various arrangements to enable different electrical circuits to be produced with them by the stylus.

8. A kit as defined in claim 7, wherein the supporting member is a printed circuit board and is surrounded on at least three sides by said connectors for receiving the electrical components. I

9. A kit including a supporting member, a stylusactuated device enabling various electrically conductive pathways to be formed by a stylus, a plurality of electrical components having uniformly spaced terminals, and a plurality of electrical connectors on the supporting member and uniformly spaced from each other according to the uniform spacing of the terminals on the electrical components, for removably receiving electrical components in various arrangements to enable different electrical circuits to be produced therewith by the stylus-actuated device.

10. A kit as defined in claim 9, wherein the stylusactuated device comprises a supporting member carrying at least one electrically conductive element, and a flexible sheet member carrying at least one electrically conductive element placeable on top of the supporting member with the two conductive elements facing each other, at least one of said members including a coating of insulating material to insulate the conductive elements from each other when the flexible sheet member is placed on top of the supporting member, said insulating coating being of a soft, pressure-flowable material which parts under the pressure of a stylus applied to the flexible sheet member to thereby bring the two conductive elements into contact with each other, said insulating coating also being tacky to hold the two conductive elements in contact with each other upon removing the pressure of the stylus, said conductive elements on both of said members being in the form of discrete conductive deposits insulated from the others on all sides by narrow interruptions between them, such that a conductive pathway is formed along the line of the stylus pressure by the successive electrical contacts between the conductive deposits of one member bridging the in- I the separation of the two members. 

1. An electrical device comprising a supporting member carrying at least one electrically conductive element, and a flexible sheet member carrying at least one electrically conductive element placeable on top of the supporting member with the two conductive elements facing each other, at least one of said members including a coating of insulating material to insulate the conductive elements from each other when the flexible sheet member is placed on top of the supporting member, said insulating coating being of a soft, pressure-flowable material which parts under the pressure of a stylus applied to the flexible sheet member to thereby bring the two conductive elements into contact with each other, said insulating coating also being tacky to hold the two conductive elements in contact with each other upon removing the pressure of the stylus, said conductive elements on both of said members being in the form of discrete conductive deposits insulated from the others on all sides by narrow interruptions between them, such that a conductive pathway is formed along the lIne of the stylus pressure by the successive electrical contacts between the conductive deposits of the two members, the conductive deposits of one member bridging the interruptions of the other along the line of movement of the stylus, said conductive pathway being erasable by the separation of the two members.
 2. An electrical device as defined in claim 1, wherein said supporting member is a printed circuit board.
 3. An electrical device as defined in claim 1, wherein said insulating coating comprises wax.
 4. An electrical device as defined in claim 1, wherein the discrete conductive deposits are of polygonal shape, the deposits of one member being rotationally displaced to the deposits of the other member.
 5. An electrical device as defined in claim 1, further including a plurality of electrical terminals carried by the supporting member for connection to electrical components each of said terminals being connected to one of said conductive deposits of the supporting member enabling electrical circuits to be traced by the stylus to various component terminals.
 6. An electrical device as defined in claim 5, wherein said electrical terminals are uniformly spaced connectors for removably receiving various electrical components in selected arrangements to enable different electrical circuits to be produced with them by the stylus.
 7. A kit including the electrical device as defined in claim 6, and a plurality of electrical components having uniformly spaced electrical terminals according to the uniform spacing of the connectors in said electrical device, said components being selectively receivable in the connectors in various arrangements to enable different electrical circuits to be produced with them by the stylus.
 8. A kit as defined in claim 7, wherein the supporting member is a printed circuit board and is surrounded on at least three sides by said connectors for receiving the electrical components.
 9. A kit including a supporting member, a stylus-actuated device enabling various electrically conductive pathways to be formed by a stylus, a plurality of electrical components having uniformly spaced terminals, and a plurality of electrical connectors on the supporting member and uniformly spaced from each other according to the uniform spacing of the terminals on the electrical components, for removably receiving electrical components in various arrangements to enable different electrical circuits to be produced therewith by the stylus-actuated device.
 10. A kit as defined in claim 9, wherein the stylus-actuated device comprises a supporting member carrying at least one electrically conductive element, and a flexible sheet member carrying at least one electrically conductive element placeable on top of the supporting member with the two conductive elements facing each other, at least one of said members including a coating of insulating material to insulate the conductive elements from each other when the flexible sheet member is placed on top of the supporting member, said insulating coating being of a soft, pressure-flowable material which parts under the pressure of a stylus applied to the flexible sheet member to thereby bring the two conductive elements into contact with each other, said insulating coating also being tacky to hold the two conductive elements in contact with each other upon removing the pressure of the stylus, said conductive elements on both of said members being in the form of discrete conductive deposits insulated from the others on all sides by narrow interruptions between them, such that a conductive pathway is formed along the line of the stylus pressure by the successive electrical contacts between the conductive deposits of one member bridging the interruptions of the other along the line of movement of the stylus, said conductive pathway being erasable by the separation of the two members. 